量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.

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There are various high-energy charged particles in space. At aviation altitude (8-12km), aircraft crew and passengers are exposed to secondary cosmic radiations as well as primary particles; the secondary radiations are produced by collision of high-energy cosmic protons with the atmosphere and wall materials of an aircraft. It is thus important to assess their exposure to cosmic radiation in view of radiological protection. Until now, various personal dosimeters have been developed, photoluminescence dosimeters (PLD), thermoluminescence dosimeters (TLD), nuclear track detectors (e.g. CR-39) and electronic dosimeters. However, dosimeters which are suitable for measurement of cosmic radiation are still to be investigated. We have thus tried to design a dosimeter using new materials sensitive to energetic neutrons (0.1MeV-1GeV), i.e. the main components of cosmic radiation. In this work, we discuss the possibility of a photochromic gel of titanium oxide as a personal dosimeter. Titanium oxide is well known as a photocatalyst. Ti3+ is produced by ultraviolet (UV) irradiation of titanium oxide particles and indicates a deep blue color. Therefore, transparent titanium oxide gel will change its color to deep blue following production of Ti3+. If UV irradiation of the titanium gel stops, bleaching occurs; the deep blue coloration gradually disappears as storage time passes and the titanium oxide gel becomes transparent again. The coloration and bleaching are reversible and can be repeated many times. This property of reversible coloration, which is called "photochromism", relates to energy transitions of electrons. Therefore, we considered photochromic titanium oxide gel to be an effective material for a dosimeter, based on the technique of electron spin resonance (ESR). We also expect that the property of photochromism can be used as a real-time monitor by exploiting this colorization. As the first step in the dosimeter development, we investigate ESR signals from a synthesized photochromic titanium oxide gel irradiated with X-rays. From the results, although coloration, as seen for UV radiation, was not observed for X-rays, a hole trap that is ascribable to hydroxyl radical was produced and it was active for ESR. Synthesized titanium oxide gels therefore could be used as an ESR dosimeter for X-ray radiation.